For the first time, many New Who fans experienced a Regeneration when the Ninth Doctor gave way to his Tenth incarnation, played by David Tennant. Rose returns home with a strange looking man who insists he is the Doctor, before he passes out.  Now the Earth is under attack by an alien race, and the Doctor can't be roused. Prime Minister Harriet Jones and UNIT try to handle the menace on their own, and Rose even gives it a go, but the Doctor wakes up just in time to play the role of Earth's Champion, even as he tries to figure out who he is this go-round.